Method of removing nitrogen oxides from flue gases

Abstract

For the catalytic removal of nitrogen oxides ( 2 ) from flue gases of combustion furnaces ( 1 ) which use hydrogen (H 2 ) is used as reducing agent and the reaction is conducted at a temperature of below 150° C.

1 . In a method for the selective catalytic removal of nitrogen oxides from oxygen-containing flue gas of a combustion furnace in the presence of a reducing agent, the improvement wherein the reducing agent is hydrogen, and the catalytic removal is conducted at a temperature below 150° C. in contact with a hydrogen reduction catalyst.  
     
     
         2 . A method according to  claim 1 , wherein the catalytic removal of the nitrogen oxides is carried out directly at an exit waste heat flue of the combustion furnace.  
     
     
         3 . A method according to  claim 1 , wherein the catalytic removal of the nitrogen oxides is conducted in a separate reactor downstream of the waste heat flue.  
     
     
         4 . A method according to  claim 1 , wherein flue gases of at least two combustion furnaces are combined and together are freed from nitrogen oxides.  
     
     
         5 . A method according to  claim 1 , wherein in at least one combustion furnace in an olefin plant, a hydrogen plant, or a synthesis gas plant in which hydrogen is a process gas, and the latter hydrogen is used as the reducing agent for nitrogen oxide removal.  
     
     
         6 . A method according to  claim 5 , wherein the hydrogen used as reducing agent is cleaned up downstream of the catalytic nitrogen oxide removal via a membrane method and/or a pressure-swing adsorption method, reused and/or fed to the nitrogen oxide removal.  
     
     
         7 . A method according to  claim 1 , conducted under the following operating conditions  
       
         
           
                 
                 
               
                     
                     
                 
                     
                     
                 
                     
                   Range 
                 
                     
                     
                 
                     
                 
                 
                 
                 
               
                     
                   Catalyst volume- 
                   40,000-160,000 l/h 
                 
                     
                   related flue gas 
                 
                     
                   velocity: 
                 
                     
                   Temperature: 
                   120-150° C. 
                 
                     
                   NO x : 
                   75-2500 ppmV 
                 
                     
                   O 2 : 
                   1.7-5.5% by 
                 
                     
                     
                   volume 
                 
                     
                   H 2 : 
                   500-10,000 ppmV 
                 
                     
                   NO x  conversion: 
                   80-99% 
                 
                     
                     
                 
                     
                     
                 
             
                
                
                
                
               
               
                
               
            
             
                
                
                
                
                
                
                
                
                
                
                
               
            
           
         
       
     
     
         8 . A method according to  claim 7 , conducted at 135-145° C.  
     
     
         9 . A method according to  claim 7 , wherein said catalyst volume-related flue gas velocity is 40,000-100,000 l/h.  
     
     
         10 . A method according to  claim 8 , wherein said catalyst volume-related flue gas velocity is 40,000-100,000 l/h.  
     
     
         11 . A method according to  claim 7 , wherein the catalyst comprises platinum or palladium on a substrate.  
     
     
         12 . A method according to  claim 7 , wherein the catalyst comprises platinum on a substrate.  
     
     
         13 . A method according to  claim 12 , wherein the substrate comprises MgO—CeO.  
     
     
         14 . A method according to  claim 10 , wherein the catalyst comprise platinum on a substrate.  
     
     
         15 . A method according to  claim 14 , wherein the substrate comprises MgO—CeO.  
     
     
         16 . A method according to  claim 15 , wherein the catalytic removal of the nitrogen oxides is carried out directly at an exit waste heat flue of the combustion furnace.  
     
     
         17 . An integrated plant comprising means for providing hydrogen, a combustion chamber, means for containing catalyst located downstream and integral with said combustion chamber and conduit means connecting said means for producing hydrogen with said means for containing catalyst.